1. Technical Field
This disclosure relates generally to noise attenuation and, more particularly, to an acoustic panel (sometimes also referred to as “an acoustic liner”) for attenuating noise generated by, for example, a gas turbine engine for an aircraft propulsion system.
2. Background Information
Acoustic panels may be used in various applications to attenuate noise. An acoustic panel, for example, may be configured with a nacelle of an aircraft propulsion system to attenuate noise generated by a gas turbine engine. Such an acoustic panel typically includes a honeycomb core connected between a perforated face skin and a solid, non-perforated back skin. The honeycomb core includes a plurality of resonating chambers. These resonating chambers are tuned by selecting a desired chamber length and, thus, core thickness that corresponds to a specific target frequency of noise to be attenuated. Increasing the core thickness, for example, will typically tune the resonating chambers for attenuating lower frequency noise. Conversely, decreasing the core thickness will typically tune the resonating chambers to attenuate higher frequency noise.
Recent trends in aircraft engine design such as higher bypass ratios, larger fan diameters, slower rotating fans and/or fewer number of fan blades have resulted in those aircraft engines generating relatively low frequency noise. Relatively strict space constraints (e.g., loft envelope) for those engines, however, typically limit or prohibit increasing the thickness of an acoustic panel to tune its resonating chambers for such relatively low frequency noise. There is a need in the art therefore for an acoustic panel operable to attenuate relatively low frequency noise while utilizing the same or less space than previous acoustic panels. There is a further need to provide a panel configuration capable of reducing panel assembly time, complexity and cost.